Method and installation for continuously preparing caseinate

ABSTRACT

The invention provides a method of continuously preparing caseinate from milk proteins in non-soluble powder form in an extruder machine having two co-rotating and interpenetrating screws into which water and an alkaline reagent are introduced, and the mixture formed by the milk proteins, the water, and the alkaline reagent is subjected to a plurality of steps of kneading under pressure and of shearing with the temperature rising to obtain at the outlet from the extruder machine a caseinate paste, the caseinate paste is cooled to bring its temperature to below 20° C., a continuous thin sheet of caseinate paste is formed, and the sheet is cut up into a plurality of parallel strips, and these strips are cut up into small-sized pieces of caseinate. The invention also provides an installation for continuously preparing caseinate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is filed under the provisions of 35 U.S.C. §371 basedon International Application No. PCT/FR01/00133 filed Jan. 16, 2001,claiming the priority of French application 00/00604 filed Jan. 18,2000, each of which is incorporated herein by reference.

The present invention relates to a method and to an installation forcontinuously preparing caseinate from casein formed by milk proteins innon-soluble powder form.

BACKGROUND OF THE INVENTION

Milk is used as raw material for fabricating various products usable inthe chemical or food industries.

In particular, it is known to extract casein by precipitation, whichcasein is then transformed, for example into a jelling agent suitablefor use in particular in making soups, desserts, ices, yogurts, or porkbutchery products, or indeed for use in industries other than the foodindustry.

Nevertheless, in order to be usable, casein must initially betransformed into soluble caseinate.

To do this, caseinate is manufactured from casein, i.e. from milkproteins which are subjected to chemical transformation to enable themto absorb water.

Various categories of caseinate exist, including sodium caseinate andcalcium caseinate. Sodium caseinate is the result of kneading casein,sodium hydroxide, and water, while calcium caseinate is the result ofkneading casein, ammonium hydroxide, calcium hydroxide, and water, andpossibly also ammonia.

Until now, the chemical reaction has been performed in a reactor in thepresence of a large quantity of water and after several minutescaseinate is obtained which then needs to be dried in order to obtain apowder that presents poor solubility.

Installations that have been used until now for making caseinate arethus bulky and require large reactors and large dryers and suchinstallations consume large quantities of water and of energy.

Furthermore, the installations that have been used up until now requirenumerous handling operations between various workstations.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the invention is to propose a method and an installationfor continuously preparing caseinate without interruption in themanufacturing line and making it possible to obtain caseinate thatpresents excellent solubility and a high degree of chemical neutrality,while simultaneously reducing energy consumption and the varioushandling operations needed in order to obtain this type of product.

The invention thus provides a method of continuously preparingcaseinate, the method comprising the following steps:

-   -   milk proteins in non-soluble powder form are introduced        continuously into an extruder machine having two co-rotating and        interpenetrating screws rotated about parallel axes inside a        sheath of elongate shape;    -   a first transport step is performed in the sheath of the        extruder machine in which the milk protein powder is transported        with water, and an alkaline reagent is introduced into the        sheath at the end of this first step;    -   the mixture constituted by the milk proteins, the water, and the        alkaline reagent is subjected to first intense kneading under        pressure with a rise in temperature to initiate the chemical        reaction between the milk proteins and the alkaline reagent;    -   a second transport step is performed in the sheath during which        the mixture is transformed while the chemical reaction continues        and the temperature of the mixture rises;    -   the mixture is subjected to second intense kneading under        pressure and to intense shear in order to finish off the        chemical reaction with the temperature of the mixture rising so        as to cause the mixture to melt and so as to obtain a viscous        caseinate paste;    -   a third transport step is performed in which the caseinate paste        is transported and cooled with a degassing operation being        performed at the beginning of this step to reduce and adjust the        temperature and the viscosity of the caseinate paste;    -   the caseinate paste is subjected to a final kneading and to heat        exchange with said paste being cooled;    -   a fourth transport step is performed together with cooling heat        exchange to maintain the caseinate paste at a temperature lying        in the range 70° C. to 95° C.;    -   the caseinate paste is extruded at said temperature with a        moisture content lying in the range 30% to 40% to form a        continuous strand of caseinate paste at the outlet from the        extruder machine;    -   a continuous thin sheet of caseinate paste is formed from the        strand and said sheet of caseinate is simultaneously cooled to a        temperature below 20° C.;    -   the sheet is cut longitudinally into a plurality of parallel        strips; and    -   the strips are cut up into small-sized pieces of caseinate.

The invention also provides an installation for continuously preparingcaseinate, the installation comprising:

-   -   an extruder machine comprising two co-rotating and        interpenetrating screws rotated about parallel axes inside a        sheath of elongate shape provided with intersecting bores and        defining in succession from an upstream end to a downstream end:        -   a zone for continuous introduction of milk proteins in            non-soluble powder form into the sheath and for transporting            said milk protein powder;        -   a zone for transporting the milk protein powder and for            introducing water and an alkaline reagent into the sheath at            the end of said zone;        -   a first zone for intense kneading under pressure of the            mixture formed by the milk proteins, the water, and the            alkaline reagent, with the temperature of the mixture rising            to initiate the chemical reaction between the milk proteins            and the alkaline reagent;        -   a zone for transporting the mixture, in which zone the            chemical reaction continues and the temperature of the            mixture rises;        -   a second zone for intense kneading under pressure and for            intense shear, finishing off the chemical reaction with the            temperature of the mixture rising so as to cause said            mixture to melt and so as to obtain a viscous caseinate            paste;        -   a zone for transporting and cooling the caseinate paste with            a degassing orifice being provided through the sheath            opening out into said intersecting bores at the beginning of            said zone so as to reduce and adjust the temperature and the            viscosity of said caseinate paste;        -   a third zone for kneading and heat exchange with said paste            being cooled;        -   a zone for transport and heat exchange with cooling so as to            maintain the caseinate paste at a temperature lying in the            range 70° C. to 95° C.; and        -   a die for extruding the caseinate paste at said temperature            and with a moisture content lying in the range 30% to 40% to            form a continuous strand of caseinate paste at the outlet            from the extruder machine;    -   means for continuously forming a thin sheet from said strand and        for cooling the caseinate paste to a temperature below 20° C.;    -   means for longitudinally cutting up the sheet into a plurality        of parallel strips; and    -   means for cutting said strips transversely into small-sized        pieces of caseinate.

According to other characteristics of the invention:

-   -   the screws of the extruder machine present varying pitches in        the transport zone;    -   the screws of the extruder machine are formed in the first        kneading zone by three-lobe elements in the form of isosceles        triangles with truncated vertices so as to cause the mixture to        pass in controlled manner, the three-lobed elements of each        screw being offset relative to one another and said three-lobed        elements of the two screws interpenetrating between one another;    -   the screws of the extruder machine are formed in the second        kneading zone by threads of reverse pitch whose edges are        provided with openings regularly distributed about their axes,        the openings in each thread being offset relative to the        openings of the adjacent threads;    -   the screws of the extruder machine are formed in the third        kneading zone by two-lobed elements of lozenge shape with        truncated vertices to enable the caseinate paste to pass through        in controlled manner, the two-lobed elements of each screw being        offset from one another by 90°, and said two-lobed elements of        the two screws interpenetrating between one another;    -   the means for forming the continuous sheet of caseinate paste        and for cooling said paste are formed firstly by two parallel        rollers, each provided with a circuit for circulating cooling        fluid and leaving between them a gap through which the caseinate        paste flows, and secondly by an endless transporter belt placed        beneath one of the rollers and covering substantially half of        the outside surface of said roller, said transporter belt and        said roller leaving between them a passage through which the        caseinate paste flows;    -   the means for cutting the sheet longitudinally into a plurality        of parallel strips are formed by two parallel rollers extending        perpendicularly to the travel direction of the sheet, one of the        rollers having circular cutting blades that are parallel to one        another; and    -   the means for cutting the strips transversely into pieces are        formed by cutting blades extending perpendicularly to the travel        direction of said strips and rotated by a horizontal shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention appear from thefollowing description made with reference to the accompanying drawings,in which:

FIG. 1 is a diagrammatic section view in a vertical plane containing theaxis of a screw in an extruder machine of an installation forcontinuously preparing caseinate in accordance with the invention;

FIG. 2 is a section on line 2—2 of FIG. 1;

FIG. 3 is a diagrammatic perspective view of a segment of the screw ofthe extruder machine in the first kneading zone;

FIG. 4 is a diagrammatic perspective view of a segment of the screw ofthe extruder machine in the second kneading zone;

FIG. 5 is a diagrammatic perspective view of a segment of the screw inthe third kneading zone;

FIG. 6 is a diagrammatic elevation view of means for cooling and cuttingthe caseinate paste at the outlet from the extruder machine in theinstallation for continuously preparing caseinate in accordance with theinvention;

FIG. 7 is a diagrammatic axial section view showing one embodiment of acooling circuit for a roller in the cooling means; and

FIG. 8 is a diagrammatic perspective view of the means for cutting upthe caseinate paste.

MORE DETAILED DESCRIPTION

FIGS. 1 to 6 are diagrams showing an installation for continuouslypreparing caseinate from milk proteins in non-soluble powder form.

In general, this installation comprises:

-   -   an extruder machine 10 for transforming milk proteins in        non-soluble powder form into a viscous caseinate paste at a        temperature lying in the range 70° C. to 95° C. and possessing        moisture content lying in the range 30% to 40%;    -   means 50 for continuously forming a sheet of caseinate paste and        cooling said paste to a temperature below 20° C.; and    -   means for cutting up the sheet into a plurality of parallel        strips and then cutting up the strips into small-sized pieces of        caseinate.

As shown in FIGS. 1 and 2, the extruder machine 10 is of the type havingtwo co-rotating screws that interpenetrate, comprising two screws 11 and12 inside an elongate enclosure forming a sheath 13 which envelops them,the screws being driven in rotation about their axes by a motor and gearbox unit (not shown).

The screws 11 and 12 are provided in particular with helical threads orwith elements for processing the matter introduced into the sheath 13 ina manner described below, the screws meshing one in the other while theinside wall of said sheath 13 forms two intersecting cylindrical lobesof inside diameter that is slightly greater than the outside diameter ofthe threads and of the processing elements.

The two screws 11 and 12 are driven with the same speed of rotation andin the same direction so that the two screws are identical, the threadsand the processing elements being merely offset relative to one another.

As shown in FIG. 2, the screws 11 and 12 are advantageously constitutedby fluted shafts, respectively referenced 14 and 15 having screwsegments stacked thereon.

The inside bores of these screw segments are fluted in complementarymanner to the shafts, while the outside portions thereof are providedwith helical threads or with material-processing elements of differingpitch and configuration depending on the segment in question for thepurpose of processing and transporting said material.

It is thus possible to have available quite a large number of segmentsof different configurations depending on the type of processing to beperformed on the material.

The extruder machine 10 shown in FIG. 1 comprises a zone A forcontinuously introducing milk proteins in non-soluble powder form intothe sheath 13 and for transporting these milk proteins downstream withinsaid extruder machine 10.

In zone A, the sheath 13 is pierced at its end which is upstreamrelative to the material travel direction, by means of a feed orifice 16surmounted by a hopper 17 into which the milk protein powder is pouredcontinuously, e.g. as dispensed by a measuring-out device, not shown.

In the introduction zone A, the screws 11 and 12 are provided withlarge-pitch threads 18 in order to transport the milk protein powderintroduced via the orifice 16 which is broadly open to both screws 11and 12, and in order to distribute said powder between the screwthreads.

Thus, the milk protein powder is transported towards the downstream endof the extruder machine 10 in a zone B which comprises a first segmentB1 in which the screws 11 and 12 are provided with large-pitch threads19 and a second segment B2 in which the screws 11 and 12 are providedwith threads 20 at a tight pitch.

The milk protein powder is thus transported through the first segment B1of the zone B and then through the second segment B2 where water and analkaline reagent are injected.

To this end, the sheath 13 is pierced by an orifice 21 connected viarespective ducts 22 and 23 to means for injecting water and the alkalinereagent.

The alkaline reagent is constituted by sodium hydroxide or lime and thepercentage of water plus caseinate relative to the alkaline reagent liesin the range 90% to 97%.

The mixture constituted by milk proteins, water, and alkaline reagentsis transported by the screws 11 and 12 through a first kneading zone Cin which the mixture is subjected to intense kneading under pressure.

For this purpose, in the zone C the screws 11 and 12 are constituted, asshown in FIG. 3, by juxtaposed three-lobed elements 24 in the form ofisosceles triangles with truncated vertices so as to cause the mixtureto be passed in controlled manner towards the downstream end of theextruder machine.

As shown in FIG. 3, the three-lobed elements 24 of each screw 11 and 12are offset relative to one another and are also offset from one screw tothe other so as to engage in one another and thus perform intense mixingand kneading of the milk protein powder together with the water and thealkaline reagent.

Because of this intense kneading, the temperature of the mixture risesthus enabling the chemical reaction between the milk proteins and thealkaline reagent to begin.

By way of example, the milk protein powder is introduced into theextruder machine 10 at ambient temperature of about 20° C., and onleaving the kneading zone C, the mixture is at a temperature of about80° C.

At the outlet from the first kneading zone C, the mixture is transferredinto a zone D in which the screws 11 and 12 are provided with largepitch threads 25 leading to a second kneading zone E in which kneadingis performed under intense shear and pressure.

As shown in FIG. 4, the screws 11 and 12 in the zone E are constitutedby threads 26 of reverse pitch with peripheral edges provided withopenings 27 that are regularly distributed around the axis of thecorresponding screw.

The openings 27 in each of the threads 26 are offset relative to theopenings in the adjacent threads.

The openings 27 in the threads 26 control the rate at which the mixtureflows downstream, thereby determining a level of braking in this zone Eand a compression force upstream therefrom.

This leads to a high level of shear which homogenizes the mixture andfinishes off the chemical reaction with an increase in the temperatureof the mixture so as to cause it to melt and obtain a viscous paste ofcaseinate.

The mixing and shear operation in zone E causes the mixture to heat up,with a large fraction of the mechanical work being converted intothermal energy.

By way of example, the temperature of the mixture on leaving the zone Eis about 90° C.

Following the second kneading and shear zone E, the screws 11 and 12 ofthe extruder machine define a transport and cooling zone F for thecaseinate paste.

In this zone F, the screws 11 and 12 are formed of a plurality ofsegments of different pitches, a first segment F1 having threads 28 at atight pitch, a second segment F2 having threads 29 at a large pitch, athird segment F3 having threads 30 at a tight pitch, and a fourthsegment F4 having threads 31 at a large pitch.

At the beginning of the zone F, the sheath 13 of the extruder machine 10has a degassing orifice 32 which opens out into the intersecting boresof said sheath 13.

After the caseinate paste has passed through the zone E where it issubjected to intense kneading under pressure and shear, the caseinatepaste is subjected in segments F1 and F2 of the zone F to decompressionsuch that the gas contained in said paste escapes via the orifice 32.

While it is being transferred along the zone F, the caseinate paste iscooled so as to keep it at a temperature lying in the range 80° C. to95° C., which also serves to adjust its viscosity.

On leaving the transport zone F, the caseinate paste passes through athird kneading zone G in which it is kneaded and exchanges heat withcooling being provided to keep its temperature below 95° C.

As shown in FIG. 5, the screws 11 and 12 are constituted in the zone Gby two-lobed elements 33 in the form of lozenges with truncated androunded vertices so as to cause the caseinate paste to pass incontrolled manner between said two-lobed elements 33 and the inside wallof the sheath 13.

The two-lobed elements 33 on any one screw are offset at 90° from oneanother and they are also offset at 90° between the two screws so thatthey engage in one another.

The caseinate paste is then transferred via a transport and heatexchange zone H to the outlet from the extruder machine 10.

In the zone H, the screws 11 and 12 are provided with threads 34 at atight pitch.

As it passes through the zones G and H, the caseinate paste is cooled soas to be maintained at a temperature lying in the range 70° C. to 95° C.

By way of example, the caseinate paste is cooled as it is transferredalong the extruder machine 10 by means of a circuit formed in the wallof the sheath 13 and in which a cooling fluid circulates.

While milk protein is being processed in the extruder machine 10 toobtain caseinate paste, it is necessary for the temperature of thematerial to be controlled to ensure that it does not exceed 95° C. sinceat higher temperatures the chemical reaction does not take place undergood conditions and spots of burning can appear in the caseinate paste.

In addition, in order to facilitate processing of the caseinate pasteafter it has passed through the extruder machine, it is preferable forthe temperature of the caseinate paste at the outlet of the machine tobe controlled.

The extruder machine 10 is fitted at its downstream end in the materialflow direction with an extrusion zone I formed by a die 35 so that thecaseinate paste leaves said extruder machine in the form of a continuousstrand 40.

On leaving the die 35 the caseinate paste is at a temperature lying inthe range 70° C. to 95° C., and its moisture content lies in the range30% to 40%.

By way of example, the extruder machine 10 presents the configurationgiven in the following table:

Zones A B1 B2 C D E F1 F2 F3 F4 G H Length 150 150 50 DM 200 CF 50 20050 200 DM 525 of screws Screw 100 100 50 100 50 100 50 100 50 pitch

The strand 40 of caseinate paste leaving the extruder machine 10 istransformed in the forming means 50 into a continuous thin sheet 41derived from said strand 40. These means 50 also cool the caseinatepaste to a temperature of less than 20° C.

As shown in FIG. 6, the means 50 comprise two parallel rollersreferenced 51 and 52 each provided with a circuit for circulatingcooling fluid and leaving between them a gap 53 through which thecaseinate paste flows. The means 50 also comprise an endless transporterbelt 54 placed beneath one of the rollers, and in the embodiment shownin FIG. 6, placed beneath the roller 52.

The transporter belt 54 covers substantially half the outside surface ofthe roller 52, and said transporter belt 54 with said roller 52 leavesbetween them a passage through which the caseinate paste flows so as toform the sheet 41.

In the embodiment shown, the roller 51 is smaller in diameter than theroller 52 and the axis of the roller 51 is placed higher than the axisof the roller 52, so that while the caseinate paste flows it comes intocontact with substantially two-thirds of the outside surface of theroller, thereby enabling its temperature to be brought progressively tobelow 20° C., thereby making it easier to cut up subsequently.

FIG. 7 is a diagram showing one possible embodiment of the coolingcircuit for the roller 52, the cooling circuit of the roller 53 beingidentical.

As shown in this figure, the cooling circuit is constituted byperipheral channels 55 extending parallel to the axis of the roller andconnected via respective radial channels 56 a and 56 b to an inletchannel 57 on the axis of the roller 52, and to an outlet channel 58 forsaid fluid likewise disposed on the axis of the roller 52 concentricallyabout said inlet channel 57.

In the embodiment shown in FIG. 7, the radial channels 56 a are disposedsubstantially in the middle of the roller 52 so that the cooling fluidentering via one end of the inlet channel 57 passes to both ends of theperipheral channels 55 and this cooling fluid is removed from each endof the roller 52.

The rollers 51 and 52 have a non-stick coating made up of a layer thatis hard and slightly rough, for example a layer of ceramic, or carbide,of a metal or an alloy, and coated in a non-stick polymer, for example afluorine-containing polymer.

After passing between the roller 52 and the endless transporter belt 54,the sheet of caseinate 41 is of constant thickness lying in the range 2millimeters (mm) to 3 mm.

The sheet 41 is transferred by a transporter belt 55 to the cutting-upmeans 80.

As shown in FIG. 8, the sheet 41 of caseinate paste is transferred intothe cutting-up means 80 by means of the transporter belt 55 and a driveroller 56 placed above said transporter belt 55 and having on its outersurface ridges that enable said sheet 41 to be driven in translation.

The sheet 41 is cut into parallel strips by means of two parallelrollers respectively referenced 81 and 82 extending perpendicularly tothe travel direction of the sheet 41.

In the embodiment shown in FIG. 8, the top roller 81 has circularcutting blades 83 that are parallel to one another.

The bottom roller 82 has slots 84 in register with the circular blades83 so that as the sheet 41 passes between the two rollers 81 and 82, thecircular blades 83 penetrate into the slots 84, thereby cutting up thesheet 41 longitudinally into strips 42 of caseinate paste extendingparallel to one another.

Thereafter, the strips 42 of caseinate paste are cut up into pieces ofsmall dimensions by means of a cutting blade 85 extending perpendicularto the travel direction of the strips 42 and rotated by a horizontalshaft 86.

As shown in FIG. 6, during rotation of the cutting blades 85, the strips42 of caseinate paste are pressed against a deflector 87, therebyenabling said strips to be held so as to enable the cutting blades 85 tocut said strips into pieces.

The pieces as cut up in this way are recovered in a receptacle 88.

The method and the installation of the invention enable milk proteins tobe transformed into caseinate paste by chemical reaction, and it alsoserves to cool and roll the product of the chemical reaction and to cutup said product into pieces which present excellent solubility and ahigh degree of chemical neutrality.

1. A method of continuously preparing caseinate, wherein: milk proteins in non-soluble powder form are introduced continuously into an extruder machine having two co-rotating and interpenetrating screws rotated about parallel axes inside a sheath of elongate shape; a first transport step is performed in the sheath of the extruder machine in which the milk protein powder is transported with water, and an alkaline reagent is introduced into the sheath at the end of this first step; the mixture constituted by the milk proteins, the water, and the alkaline reagent is subjected to first intense kneading under pressure with a rise in temperature to initiate the chemical reaction between the milk proteins and the alkaline reagent; a second transport step is performed in the sheath during which the mixture is transformed while the chemical reaction continues and the temperature of the mixture rises; the mixture is subjected to second intense kneading under pressure and to intense shear in order to finish off the chemical reaction with the temperature of the mixture rising so as to cause the mixture to melt and so as to obtain a viscous caseinate paste; a third transport step is performed in which the caseinate paste is transported and cooled with a degassing operation being performed at the beginning of this step to reduce and adjust the temperature and the viscosity of the caseinate paste; the caseinate paste is subjected to a final kneading and to heat exchange with said paste being cooled; a fourth transport step is performed together with cooling heat exchange to maintain the caseinate paste at a temperature lying in the range 70° C. to 95° C.; the caseinate paste is extruded at said temperature with a moisture content lying in the range 30% to 40% to form a continuous strand of caseinate paste at the outlet from the extruder machine; a continuous thin sheet of caseinate paste is formed from the strand and said sheet of caseinate is simultaneously cooled to a temperature below 20° C.; the sheet is cut longitudinally into a plurality of parallel strips; and the strips are cut up into small-sized pieces of caseinate.
 2. A method according to claim 1, wherein lime or sodium hydroxide is used as the alkaline reagent.
 3. A method according to claim 1, wherein the percentage of water plus caseinate relative to the alkaline reagent lies in the range 90% to 97%. 